An X-ray CT (Computed Tomography) apparatus that is one of medical image diagnostic apparatuses reconstructs a tomographic image of an object using projection data from multiple angles that can be obtained by rotating an X-ray tube device irradiating an X-ray to the object and an X-ray detector detecting distribution of the X-ray dose transmitted through the object as the projection data around the object to display the reconstructed tomographic image. The image to be displayed on the X-ray CT apparatus draws organ shapes inside the object and is used for image diagnosis.
As a radiation detector represented by an X-ray detector used for an X-ray CT apparatus, an indirect-conversion-type detector, which is provided with a detection element in which a phosphor element such as a ceramic scintillator and a light detecting element such as a photodiode are combined, is used mainly. Also, a direct-conversion-type detector, which is provided with a semiconductor element as a detection element, has been recently used. In either type of the radiation detector, a structure in which approximately one thousands of detection element s are arranged on an arc around an X-ray focus in the rotation plane and a plurality of the detection element arrays are further arranged in the rotation axis direction is adopted. Also, a number of collimator plates are provided along the rotation axis direction on the X-ray tube device side of the X-ray detector in order to remove a scattered X-ray from an X-ray transmitted through an object. The collimator plates are made of thin metal plates that can shield an X-ray sufficiently and arranged radially toward the X-ray focus.
In a modern X-ray CT apparatus, it is promoted that the rotation speed and the number of detection element arrays are increased mainly in order to shorten an examination time. Increasing the rotation speed increases a centrifugal force applied to a collimator plate, and increasing the number of detection element arrays extends a length of a collimator plate in the rotation axis direction, which results in reducing the collimator plate strength. Therefore, as the rotation speed and the number of detection element arrays are increased, a collimator plate can be easily deformed during CT scanning. The deformed collimator plate changes an amount of X-ray incident on a detection element, which causes artifact generation on a tomographic image. The patent literature 1 discloses an X-ray detector capable of reducing the collimator plate deformation and an X-ray CT apparatus therewith.